Platable polymers

ABSTRACT

In the art of electroplating nonconductive materials, adhesion of metal to the material is enhanced by incorporating into the material from 1 to 25 percent by weight of a metal resinate. Crystalline polyolefins, such as polyethylene, polypropylene and propylene-ethylene copolymer, are modified with calcium resinate, zinc resinate, aluminum resinate, sodium resinate, potassium resinate or ammonium resinate to improve the adhesion of metal thereto.

United States Patent Poppe et al.

[151 3,655,433 [4 1 Apr. 11, 1972 [54] PLATABLE POLYMERS [72] Inventors:Wassily Popp Habet M. Khelghatian,

both of Springfield, Pa.; James E. Fitzpatrick, Naperville, Ill.

[52] U.S. Cl. ..l17/138.8 E, 260/27, 117/47 A, 117/160 R, 204/30 [51]Int. Cl ..B32b 27/32 [58] Field of Search ..204/30, 38 B; l17/l38.8 E,117/160 R; 161/216; 260/27 R [56] References Cited UNITED STATES PATENTS3,466,232 9/1969 Francisetal. ..204/30 2,837,491 6/1958 McKay ..260/273,462,288 8/1969 Schmidt et al ..l 17/138.8 E 2,689,805 9/1954 Ci'0ze etal ..1 17/160 3,201,271 8/1965 Simmons et a1 ..204/30 3,513,015 5/1970Fitzpatrick et al.... .....204/30 3,532,518 10/1970 DOttavio ..204/30OTHER PUBLICATIONS Narcus, Vacuum Metallizing, Metallizing of Plastics,Reinhold Publishing Corp., NY. Oct. 1960 Primary Examiner-William D.Martin Assistant ExaminerSadie L. Childs AttorneyRoger V. N. Powelsonand Arthur G. Gilkes [57] ABSTRACT In the art of electroplatingnonconductive materials, adhesion of metal to the material is enhancedby incorporating into the material from 1 to 25 percent by weight of ametal resinate. Crystalline polyolefins, such as polyethylene,polypropylene and propylene-ethylene copolymer, are modified withcalcium resinate, zinc resinate, aluminum resinate, sodium resinate,potassium resinate or ammonium resinate to improve the adhesion of metalthereto.

4 Claims, No Drawings PLATABLE POLYMERS This application is acontinuation-in-part of US. Ser. No. 732,545, filed May 28, 1968.

The present invention relates to polyolefin compositions and moreparticularly to polyolefin compositions which are suitable forelectroplating. In another embodiment, the present invention relates tothe modification of polyolefins to make surfaces of articles preparedfrom such polyolefin compositions improved in their utility andelectroplating.

The problem of causing ink, paint or other types of coating to adhere toa polyolefin surface is well-known. Various methods and means have beensuggested for improving the adhesion to surfaces. In general, theapproach to solving the problem of adhesion to a polyolefin surface hasbeen to modify the surface of the finished article by an oxidizingtreatment of some kind. Although some of the methods based on surfaceoxidation of a polypropylene have been proven to be satisfactory forimparting printability to a polyolefin surface such treatment, ingeneral, has found only limited success in causing a superior bondbetween the surface of the polyolefin article and metal plated onto thesurface. The electroplating of a polyolefin article in which the metalplate, having thicknesses in the range of 1 mil, is tightly bonded tothe polyolefin substrate constitutes, however, a highly desirable goalin view of the more recently developed polyolefins which can beconsidered engineering plastics and thus substitutes for zinc die castsor other metals. An electroplated metal coating having good adhesion tothe plastic substrate, furthermore, improves the structural propertiesof the plastic thereby enhancing its use as a substitute for metals. Theadvantages of using polyolefins in such applications include lower costof materials, cheaper tooling and tool maintenance, lower finishingcosts in buffing and polishing and lower shipping costs. The use ofpolyolefins, furthermore, allows greater versatility of product designand gives a more corrosion-resistant end product. In the engineering andaerospace fields, the substitution of plastics for metal can result inweight savings which is always of vital importance. Increased adhesionbetween the metal plate and the polyolefin substrate causes improvedphysical properties such as flexural modulus, impact strength andtemperature deflection.

It is known to incorporate additives into polyolefins such aspolypropylene in order to improve etching of the surface by oxidizingacids to a point at which a satisfactory metal-toplastic bond isobtained in subsequent plating operations. Such compositions are, forexample, shown in US. Pat. application Ser. No. 637,316, filed May 3,1967, by Khelghatian and Poppe, two of the inventors herein, and nowabandoned. This application discloses platable polyolefin compositionscontaining small amounts of a surfactant together with a compatiblesulfur compound, and shows that with such compositions metal-to-plasticbonds of 13-16 lbs./in. may be obtained. In order to obtain such bondsit is necessary to treat the shaped polyolefin with an oxidizing acidcontaining chromium trioxide under severe conditions, for example,minutes at 85 C. At lower temperatures more time is required to properlycondition the surface. Under these conditions severe etching takesplace, and the chromium trioxide rapidly becomes depleted.

It is an object of this invention to provide polyolefin compositionswhich can be conditioned for electroplating by treatment with anoxidizing acid for much shorter times than the previously knowncompositions, with attendant lowering of consumption of oxidizing agent.

It is a further object of the invention to provide polyolefincompositions which, when conditioned with an oxidizing acid atconventional temperatures and times, will have a metal-toplastic bondstrength far higher than can be obtained with previously knownpolyolefin compositions.

The polyolefin compositions of the present invention comprise polyolefmscontaining from 1 to percent by weight and preferably from 2 to 10percent by weight of a metal resinate such as calcium resinate, zincresinate, aluminum resinate, sodium resinate, potassium resinate, orammonium resinate. If more than 25 percent of the resinate is blendedinto the polyolefin, adhesion of metal to the substrate is improved butthe substrate loses tensile strength and becomes brittle to such anextent that it is of no commercial interest. The polyolefin may contain,and preferably does contain, a small amount of a surfactant and anorganic sulfur compound in addition to the resinate, but the resinatealone gives adequate metal-to-plastic bond strength.

The polyolefins modified by the addition of the metal resinate comprisein general all polymers obtained by the addition polymerization of ahydrocarbon containing terminal ethylenic unsaturation. Although vinylaromatic polymers can be improved for electroplating by using theabove-described additives, the polyolefins preferably employed arecrystalline polymers of aliphatic olefins such as polyethylene,crystalline polypropylene, crystalline ethylene-propylene copolymers,ethylene butenel copolymers, polybutene-l, poly (4-methylpentene-l poly(3-methylbutene-l and the like. The term polyolefin as used herein is,furthermore, intended to include copolymers of hydrocarbon monomers withcopolymerizable polar monomers in which such functional monomersconstitute up to 10 percent of the copolymer. Functional monomersfrequently employed in combination with hydrocarbon monomers are inparticular the acrylic monomers such as methyl methacrylate, ethylacrylate, and acrylonitrile and the vinyl esters such as vinyl acetate.The modified polyolefin compositions of the present invention,furthermore, can contain inert inorganic fillers such as asbestosfibers, glass fibers, carbon, silica, talc and alkaline earth saltswhich are frequently added to improve the rigidity of the polyolefm. Inaddition, the polyolefin compositions of the present invention cancontain other additives normally added to the polyolefin in order toimprove fabricability or solid state properties of such polyolefin.

The compositions of the present invention are formed by methodsheretofore employed for the addition of modifiers to a polyolefin. Suchmethods generally involve melt blending of the polymer and the additivein equipment such as extruders, stirred mixers or milling rolls.However, other methods of distributing additives in the polyolefin arenot intended to be excluded. In blending the additives with thepolyolefin, the same precautions against degradation of a polymer andadditive heretofore practiced should also be observed in the formulationof the compositions of the present invention.

The modified polyolefins of the present invention are shaped into thearticle desired to be electroplated by any of the means heretoforeemployed for the preparation of such articles inclusive of which arecompression molding and injection molding.

Although a variety of processes have been developed for theelectroplating of nonconductive surfaces and in particular plastics, thesame general steps are usually employed. Thus, the plating of articlesmade from the modified polyolefins of the present invention is generallyconducted using the following steps:

1. The surface to be plated is cleaned using a mild alkaline bath toremove oils, mold release agents, and fingerprints.

2. The alkaline material retained by the surface is neutralized using amild acid.

3. The clean surface is then chemically etched with a conditionercontaining concentrated mineral acid such as sulfuric acid and chromictrioxide or a chromate.

4. The resulting etched surface is sensitized with a readily oxidizabletin salt solution such as stannous chloride which causes tin to beabsorbed on the surface.

5. The surface is then activated or nucleated by treatment with anaqueous solution of a noble metal salt such as palladium chloride whichforms a metallic film at discrete activated sites.

6. The activated surface is subjected to electroless plating usingcopper, nickel, or cobalt as the metal. This is accomplished byimmersing a treated surface in a solution of such metal salt containingin addition to the metal salt such as copper sulfate or nickel chloride,a reducing agent such as formaldehyde, trioxymethylene and the like.Sufficient copper, nickel or cobalt is deposited on the surface of thepolyolefin article to achieve a continuous coating capable of conductingelectricity.

7. The electrodeposition of metal is then followed by conventionallyplating of the surface with copper, nickel and/or chromium or justnickel and chromium. The thickness of the electroplated coating isgenerally within the range of 0.1 to 1.5 mil.

it is, furthermore, highly desirable if not essential to rinse and cleanthe surface being treated with water between each of the steps outlinedand in some instances, it may also be desirable to dry the surfacebetween the various treating steps. Since the various outlined stepsemployed in the electroplating of nonconducting surfaces andparticularly plastic surfaces are well known in the electroplating art,no further description is deemed necessary for a full understanding ofthe present invention. The polyolefin compositions of the presentinvention can be employed in electroplating using any of the processesheretofore developed for electroplating of plastic and particularlypolyolefin surfaces.

The polyolefin compositions of the present invention are as indicatedparticularly suitable in the electroplating of articles made from thecomposition in that they give rise to a greatly improved bond strengthbetween the metal plate and the polyolefin substrate. Although theadhesion of metal plate to the substrate can be measured by varioustests, bond strength is preferably measured by the pull test in whichtwo parallel cuts are made into the plated metal coating, one half-inchapart, an additional vertical cut is made to form a tab, one end of theresulting tab then being raised sufficiently to allow gripping by atensile testing machine; the specimen is then placed into a tensile rigand the tab is pulled vertically from the surface. The force required topull the tab is measured as the bond strength. For most applications, abond strength of 6 to 10 lbs/in. is adequate, but if the plated articlein use is to be subjected to mechanical shock or extremes oftemperature, bond strengths in excess of 25 lbs/in. are desirable.

The present invention is further illustrated by the following examplesand controls in which all parts and percentages are by weight unlessotherwise indicated.

CONTROL 1 To 100 parts of crystalline polypropylene having a flow rateof 3.4 (ASTM D -l238-62T) is added 0.5 part of Triton X-l 00, acommercially available nonionic detergent of iso-octylphenylpolyethoxyethanol, 0.5 percent of dilauryl thiodipropionate, and percentTiO The polymer was melt blended in an extruder causing the additives tobe uniformly distributed throughout the polypropylene. The modifiedpolypropylene was then molded into 3 inch X 2 inch X l mil plaques whichare electroplated by the following process.

The plaques were immersed consecutively in a conditioner consisting of40 percent sulfuric acid (96 percent concentration), 39.5 percentphosphoric acid (85 percent concentration), 3 percent chromium trioxideand 17.5 percent of water to which has been added, per liter ofconditioner, 36 g. of an additive containing 64 percent of chromiumtrioxide and 36 percent of sodium hydrogen sulfate, for a period of 5minutes at 77 C.; in a stannous chloride sensitizer solution containingper liter of solution 10 g. of SnCl and 40 ml. of HCl at ambienttemperatures of l to 3 minutes; in an activator solution containing pergallon of solution 1 g. of palladium chloride and 10 ml. of l-lCl for aperiod of l to 2 minutes at ambient temperatures; and in an electrolesscopper plating solution containing per liter of solution 29 g. of coppersulfate, 140 g. of Rochelle Salt, 40 g. of sodium hydroxide and 166 g.of formaldehyde (37 percent solution) at a temperature of 70 C. for aperiod sufficient to obtain a continuous coating capable of conductingelectricity. Between each of the irnmersions described, the plaque isthoroughly rinsed with distilled water. The resulting plaque, on washingwith water, was then electroplated with copper for about minutes, at acurrent density of approximately 30 amps/sq. ft, resulting in a l milcoating of copper on the plaque. The plated plaque was not acceptabledue to blistering.

CONTROL 2 Control 1 was repeated, except that the treatment with theacid solution was for 10 minutes instead of 5. Again the plated plaquewas unacceptable because of blistering.

CONTROL 3 Control 1 was repeated, increasing the time of treatment withthe acid solution to 15 minutes. This time the plated plaque wasacceptable, and a bond strength of about 36 lbs/in. was obtained.

EXAMPLE 1 Control 1 was repeated, except that the polypropylenecontained 3.5 percent of calcium resinate containing about 4.5 percentash as CaO. The plated plaque was acceptable, and the bond strength wasabout 25 lbs/in.

EXAMPLE 2 Example 1 was repeated, except that a crystallineethylenepropylene terminal block copolymer was substituted for thepolypropylene of Example 1. A bond strength of about 19 lbs/in. wasobtained.

EXAMPLE 3 Example 1 was repeated, except that the polymer waspolyethylene containing 10 percent calcium resinate and the conditionerconsisted of 55 percent sulfuric acid, 10 percent potassium dichromate,and 35 percent water. A bond strength of about 9 lbs/in. was obtained.

EXAMPLE 4 Example 1 was repeated, except that the conditioner was theconditioner of Example 3, and the polymer contained 5 percent calciumresinate and the conditioning temperature was 60 C. A bond strength ofabout 14 lbs/in. was obtained.

EXAMPLE 5 The procedure of Example 4 was repeated, except that theconditioning temperature was increased to 70 C. A bond strength of about24 lbs/in. was obtained.

EXAMPLE 6 The procedure of Example 4 was repeated, except that theconditioning temperature was C. A bond strength of about 34 lbs/in. wasobtained.

EXAMPLE 7 The procedure of Example 4 was repeated, except that theconditioning temperature was 60 C. and the time of conditioning with theacid solution was 2 minutes. A bond strength of about 9 lbs/in. wasobtained.

EXAMPLE 8 The procedure of Example 7 was repeated, except that theconditioning temperature was increased to 70 C. A bond strength of about17 lbs/in. was obtained.

EXAMPLE 9 Repeating Example 4 at 60 C. and a conditioning time of 1minute, a bond strength of 6 lbs./in. was obtained.

EXAMPLE 10 The procedure of Example 9 was followed, except that theconditioning temperature was 70 C. A bond strength of IO lbs/in. wasobtained.

EXAMPLE 11 Example 9 was repeated, except that the conditioningtemperature was 80 C. A bond strength of about l5 lbs/in. was obtained.

EXAMPLE 12 The procedure of Example 9 was followed, except that theconditioning time was 30 seconds, and the temperature was C. A bondstrength of 10 lbs/in. was obtained.

EXAMPLE 13 If extremely high bond strengths are required, these may beobtained by increasing the conditioning time and temperature. If Example4 is repeated, with a conditioning time of 15 minutes, at 90 C. a bondstrength of 42 lbs/in. is obtained, and at C. the bond strength is 44lbs/in.

EXAMPLE l4 In this example, the polypropylene used as the base materialcontained 0.5 part of Triton" X-lOO, 0.5 percent dilaurylthiodipropionate, 5 percent TiO and 3.5 percent of zinc resinatecontaining 5.6 percent combined zinc and 1.8 percent combined calcium. Aplaque molded from this material was conditioned at 80 C. for 5 minuteswith the conditioner of Example 3, followed by the plating stepsoutlined in Control 1. A bond strength of 27 lbs/in. was obtained.Substituting zinc resinates containing 4.9 percent zinc and 1.7 percentcalcium; 8.9 percent zinc and 0.6 percent calcium; and 2.3 percent zincand 2.6 percent calcium, similar bond strengths were obtained. 3.5percent of aluminum resinate substituted for the zinc resinate gave abond strength of 25 lbs/in.

EXAMPLE l5 Incorporation of the metal resinates also appears to shortenthe time required in the electrolcss plating steps. A plaque containing5 percent calcium resinate was successively treated with the conditionerof Example 3 at 90 C. for 30 seconds, with the sensitizer of Control 1for 30 seconds, with the activator solution for 30 seconds, and with theelectroless copper plating solution for 5 minutes, a total cycle time ofonly 6.5 minutes. When subsequently electroplated, a bond strength ofabout 9 lbs/in. was realized.

As previously stated, it is preferred that the polymer to be platedcontain the surfactant and the organic sulfur compounds, but these arenot necessary, and adequate, but slightly lower bond strengths, areobtained in their absence. The TiO, added to the polymer in the examplesdoes not affect the bond strength, but does improve the surface qualityof the molded article.

EXAMPLE 16 Five percent calcium resinate was blended with polypropylenewithout adding any Triton," dilauryl thiodipropionate, or TiO Plaquesformed from this material were conditioned at C. for 5 minutes with theconditioner of Example 3, followed by the plating steps. Bond strengthsof 1 8-20 lbs/in. were obtained. Repeating this example, but with theaddition of 0.5 percent dilauryl thiodipropionate, bond strengths of22-24 lbs/in. were obtained.

What is claimed is:

1. As an article of manufacture, a substrate comprising a crystallinepolyolefin intimately mixed with from 1 to 25 percent of the polyolefinof a metal resinate, and a metal coating adherent to the substrate.

2. The article of claim 1 in which the content of metal resinate is from2 to 10 percent by weight.

3. The article of claim 1 in which the polyolefin is a crystallinepolypropylene.

4. The article of claim 1 in which the polyolefin is a crystallinepropylene-ethylene copolymer.

2. The article of claim 1 in which the content of metal resinate is from2 to 10 percent by weight.
 3. The article of claim 1 in which thepolyolefin is a crystalline polypropylene.
 4. The article of claim 1 inwhich the polyolefin is a crystalline propylene-ethylene copolymer.